Tweezers progress

Yesterday I took my new batches of frozen competent cells (B. subtilis and H. influenzae) across town to the biophysics lab, so I'll have cells there to test without needing to make fresh ones. While I was there I learned a better way to coat cover slips with poly-L-lysine, which I hope will give more reproducible attachment of competent cells. And I spent more time making microscope-slide chambers and learning about the tweezers apparatus (mostly standing by while the expert grad student made adjustments to the optics and electronics).

I also attended a seminar about DNA bending. Short fragments of double-stranded DNA (~100 bp) have been reported to circularize much more efficiently than predicted by their expected persistence length (paper by Cloutier and Widom), and one proposed explanation is the formation of tiny 'bubbles' in the DNA structure – places where several base pairs have separated although the DNA backbones remain intact. Even though such short single-stranded regions are expected to be very transient they can have a big impact on the probability that the ends of the DNA will meet, allowing DNA ligase to join them and circularize the DNA.